Maybe the distinction between being unopened and being closed is that being unopened implies a desire to be opened due to the nature of having always been closed, while being closed implies a denial of access. You can become closed, but once you have been opened you can never become unopened again.

Being unopened also implies a state of passivity; it is a neutral state of being. An outside force is the only thing that can open the unopened. But because the nature of being closed is purposeful denial of access rather than passive existence, what is closed can potentially open itself. There is the implication of choice. However, it is just as possible for an outside force to open the closed. And in certain cases this is the only way the closed can become open.